It is known that an inorganic compound has high-reflection properties, as the permittivity of the inorganic compound has a negative value in a band between TO phonon frequency (transverse optical phonon frequency) and LO phonon frequency (longitudinal optical phonon frequency) (see Non-Patent Literatures 1 and 2).
Patent Literature 1 discloses a method for determining a carrier concentration with a terahertz light reflection measuring device. By this method, a magnetic field is applied while terahertz light is being irradiated to the material to be measured. A hole coefficient is measured by observing an electric field generated by a hole effect, and a carrier concentration is determined. Also, by this method, a terahertz wave generating device that uses a femtosecond laser is used as the terahertz light source. In this terahertz wave generating device, the response time of the generated electric field is several picoseconds, and terahertz light of 0.5 to 2.0 THz in frequency is oscillated.
Patent Literature 2 discloses a method for inspecting the property information about a semiconductor material through transmittance measurement using terahertz light. By this method, transmission measurement is carried out, and the property information is identified based on absorption loss of the semiconductor.
[Patent Literature 1] Japanese Patent Application Laid-Open No. 2005-315708
[Patent Literature 2] Japanese Patent Application Laid-Open No. 2002-5828
[Non-Patent Literature 1] K. A. Maslin, C. Patel and T. J. Parker, “Far-Infrared Optical Constants of a Selection of Zincblende Structure Crystals at 300 K”, Infrared Physics, Vol. 32 (1991), P. 303-310
[Non-Patent Literature 2] Charles. Kittel, “Introduction to Solid State Physics”, Vol. 1, 7th Edition, translated by Ryousei Uno, Noboru Tsuya, Akira Morita, and Jiro Yamashita (published by Maruzen Company, Limited, 1998), P. 321-328